In all seriousness, you can never teach a child (or anyone for that matter) too much about firearms safety. We incorporated this into the PE unit of our homeschooling one year.
(1) All firearms are regarded as loaded at all times. (Alec Baldwin could tell you all about this one.)
(2) Never point your firearm at anything you do not wish to kill. (See above.)
(3) Never put your finger on the trigger until you are ready to shoot.
(4) Always be sure of your target and what is behind it.
I had some time to kill at McDonald's today (long drive-thru line), so I proceeded to clean my Ruger SR9C with a Remington Rem Oil cloth that I had in the car. A plastic straw with the cloth wrapped around it is too fat to go all the way through the barrel, so I discovered. (I waited till I got home and used an old wooden chopstick.) Be assured that I was discreet while doing this in the McDonald's line, though in my part of the country, I doubt it was the first time someone has done something like this. I keep a combination trigger lock on it (and on all my guns) at all times unless I am carrying.